He represented York County in the Legislative Assembly of New Brunswick from 1792 to 1795 and from 1796 to 1821.
Agnew was born in Virginia, the son of the Reverend John Agnew, and was educated in Glasgow, and joined the Queen's Loyal Virginia Regiment at the beginning of the American Revolution.
Agnew and his father, a chaplain for the loyalists, were captured in 1781 and released at the end of the war.
Agnew later fought with Samuel Denny Street, one of the lawyers for the slave.
This article about a member of the Legislative Assembly of New Brunswick is a stub.